Precise Tuning of Functional Group Spatial Distribution on Porphyrin Rings for Enhanced CO2 Electroreduction Selectivity

Molecular catalysts play a critical role in regulating the selectivity of electrocatalytic CO₂ reduction reaction (CO₂RR), yet the understanding of ligand function is largely restricted to modulating the electronic structure of the metal and reaction kinetics. Herein, a hydroxyl (─OH) ligand is introduced into a sterically hindered amino-porphyrin (o-TAPP) to synthesize the atropisomers porphyrin-salicylimine-Cu (o-Cu-Por-Sa) with hydrogen-bonding interactions (O─H⋯O), enabling efficient selection of CO and CH₄ under dual effects. Detailed analysis shows that the ─OH of o-Cu-Por-Sa (αβαβ) forms a noncovalent hydrogen bond with carbonate, characterized by a bond length of 2.01 Å and an angle of 27.6°, and this interaction reduces the reaction energy barrier, achieving a faradaic efficiency (FE) of 84% for CH₄. Moreover, the steric hindrance effect of the symmetric distribution of ─OH facilitates protonation reactions by preventing C-C coupling. In contrast, ─OH aggregated on o-Cu-Por-Sa (αααα) forms a pocket-like hydrogen bond grid, which restricts free CO₂ adsorption, and the rapid dissociation of *CO also interrupts the reaction. This work highlights the pivotal role of dual effects induced by ligand atropisomerization in regulating selectivity, offering new insights for the design of efficient molecular catalysts.